The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium improved to be suitable for high density magnetic recording by reducing noise generated from the magnetic recording medium and to a magnetic storage device using the same.
Studies have been made on a magnetic recording medium formed of a continuous magnetic thin film for realizing high density magnetic recording. Specifically, such a magnetic recording medium is prepared by a method wherein a thin film made of a ferromagnetic metal, Co or Co-based alloy is formed on a substrate made of a nonmagnetic material such as aluminum or glass coated with a plastic film or NiP film by radio frequency sputtering, ion beam sputtering, vacuum evaporation, electric plating or chemical plating. In the magnetic recording medium thus prepared, a microstructure of a magnetic thin film is closely related to magnetic properties. As a result, various attempts have been made to improve a magnetic layer constituting a magnetic recording medium for enhancing magnetic recording density and reproduced output.
For a longitudinal magnetic recording medium, it has been conceived that an easy magnetization axis thereof is desirable to be parallel to a substrate. On the other hand, various methods have been known to provide an underlayer between a substrate and a magnetic layer for ensuring longitudinal magnetic anisotropy. For example, U.S. Pat. No. 4,654,276 discloses a method in which a layer made of W, Mo, Nb or V is used as an underlayer for a Co--Pt magnetic layer. U.S. Pat. No. 4,652,499 discloses a method in which a V--Cr or Fe--Cr alloy material is used as an underlayer. Japanese Patent Laid-open No. Sho 63-106917 discloses a method in which a nonmagnetic layer made of Cr, Ho, Ti or Ta as an underlayer for a magnetic layer made of Co, Ni, Cr or Pt. U.S. Pat. No. 4,789,598 discloses a method in which Cr or a Cr--V alloy is effective as an underlayer for a Co--Pt--Cr layer.
When a Co-based alloy magnetic layer is formed on a substrate through an underlayer made of Cr or a Cr alloy by sputtering, the underlayer is first oriented in (100) or (110). In this case, when the Co-based alloy magnetic layer is formed on the (100) orientated layer, the easy magnetization axis thereof is parallel to the substrate; while when the Co-based alloy magnetic layer is formed on the (110) oriented layer, the easy magnetization axis thereof is substantially in parallel to the substrate, more specifically, it is inclined at about 30.degree. relative to the surface of the substrate.
For improvement in an a real density of magnetic recording, it is required to reduce noise generated from a magnetic recording medium as well as to enhance resolution of magnetic recording. In particular, when a reproducing magnetic head of a magneto-resistance (MR) type being high in read-out sensitivity, it becomes important to reduce noise of a magnetic recording medium. The prior art magnetic recording medium of a type in which the easy magnetization axis thereof is oriented in the longitudinal direction has a disadvantage that it can improve resolution of magnetic recording; however, it has a difficulty in reducing noise thereof. In particular, for an areal recording density of magnetic recording increased to 1 Gb/in.sup.2 or more, the prior art magnetic recording medium is very difficult to reduce noise thereof.